Objects which exhibit intensely fluorescent color in daylight, or when exposed to a beam of light at night are particularly useful as not only as markers, signs, and other informative and safety oriented devices, but as decorative features. Over time, however, fluorescent colored objects and objects coated with materials such as fluoresent paint, may lose their fluorescent coloration fading This effect is caused by exposure to the elements, particularly sunlight. For objects that are located outdoors for a period of time, lightfastness of the fluorescent color may determine the useful life of the object.
In addition to lightfastness, a fluorescent pigment should exhibit good color, heat stability, and friability. The fluorescent pigment should also be capable of being mixed with either the material of the object that is to be colored, or be mixed in paint or ink. Since the fluorescent dyes themselves are not generally capable of mixing with the material of the object, they are typically combined with resins or other polymeric products to provide a pigment. In conventional fluorescent pigments, the polymer component of the pigment typically acts as a carrier or solvent for the dye; the polymer and the dye associate in a "solid state solution". The conventional fluorescent dye carriers have varied compositions which are selected depending upon the dye and the use of the pigment. The use of certain polyamide polymers and polyamide-polyester copolymers as carriers for fluorescent dye have been described previously; however the polymers are first formed and then the fluorescent dye is added, to form a solid state solution of dye and polymer. While such light fast pigments are useful, upon exposure to ultra-violet light, the lightfastness of the pigments is limited.
Furthermore, where the pigment is to be used in molded plastics, resistance to plate out is desired.
It would be desirable to have a fluorescent pigment having good color, heat stability, friability, which is suitable for coloring a variety of materials, that demonstrates improved lightfastness.